There are in the prior art cargo handling systems where the support surface for the cargo has a plurality of ball transfer units positioned across the floor.
Ball transfer units for conveyor systems are known in which a load-bearing ball is seated in an essentially radially symmetric bearing unit having ball bearings in a bearing shell. The ball member of each unit is rotatably mounted in a manner to provide a low friction support surface over which the cargo can roll. In some instances, the ball members are spring loaded so as to provide for limited up and down movement of the ball members, so that the loads can be properly distributed over a number of ball transfer units.
Ball transfer units of this sort are used in conveyor systems, many identical ball units being mounted in ball platforms or beds to form a field over which objects to be transported, such as containers, can be pushed. Such ball units are commonly employed in cargo aircraft, where low weight and high reliability are important considerations.
Such cargo handling systems have been used in connection with aircraft where fast and convenient cargo handling is required, and the cargo handling must be accomplished in a relatively limited space. While such cargo handling systems in the past have been used effectively, there is a continuing need to improve the design of these systems relative to convenience of servicing and repair, and overall effectiveness of operation.
There are a number of such ball transfer units which are shown in the patent literature, and these are discussed below.
Karmin, WO 79/00940 discloses a ball handling device comprised of a body inside which is located a funnel-shaped support at the opening of which a ball is arranged. A threaded cover provided with a flange is intended to retain the ball when a pressure fluid flows into the support. When the threaded cover is removed, the entire unit is broken down into components which does not lend itself to the orderly disassembly which is important where large numbers of small roller balls are present.
Sundseth, U.S. Pat. No. 5,098,308 relates to a load bearing ball held in the bearing unit by a securing apparatus. The bearing unit has a supporting structure that enables the bearing unit to be fixed in an opening of a carrier plate in such a way that it can support a load. Detents are provided to lock the unit in the opening against the load direction. The bearing shell can be constructed integrally with the supporting structure as a semielastic formed element. This arrangement does not lend itself of ready removal of the ball transfer unit as a discrete unit from the supporting structure for cleaning or servicing.
Huber, U.S. Pat. No. 5,033,601 discloses a conveyor ball unit in which locking elements on the ball cover or guide perform a dual function: on the one hand, locking shoulders are present which serve to hold the mounting shell, the roller balls, the conveyor ball and the ball cover together, while on the other hand they also perform the function of holding the conveyor ball transfer unit in the mounting opening in the conveyor bed or platform. In the installed condition, the locking shoulders also engage under the edge of the mounting opening in the conveyor bed to secure the conveyor ball transfer unit in position. This structure does not lend itself to the removal of the ball transfer unit from the bed in one piece for servicing and cleaning.
Hinman, U.S. Pat. No. 3,739,894, shows a ball transfer unit where the main ball is supported by a plurality of smaller ball bearings. The cover member has an upper in turned shoulder which engages a flange in the ball race assembly to hold the main cargo engaging ball in place. There is a compression spring which urges the ball upwardly toward its upper support position. This type of securing arrangement for holding the ball cover to bearing race assembly is not easily undone for servicing.
Gorges, U.S. Pat. No. 4,696,583, discloses a ball transfer unit having an upper ball retaining portion in the form of a generally cylindrical side wall that defines a ball receiving recess. The upper half of the wall is formed with four evenly spaced vertical slots that separate the upper portion of the side wall into four expandable sections. The upper edge of the side wall is formed with a circumferential flange that has an inwardly extending circumferential lip to retain the ball in the recess. The outer edge of the flange fits against the upper inner surface of a surrounding collar which, in turn, is held in the conveyor bed by a retaining spring. This device is quite complicated to take apart and re-assemble.
Evarts, U.S. Pat. No. 3,920,290 discloses a ball transfer unit comprising a ball, a housing, means for rotatably supporting the ball within the housing and means for retaining the ball on the support means and within the housing. No provision is made for disassembly for servicing.